CD40 is a cell surface phosphorylated glycoprotein that is expressed on a variety of cell types, including B cells, B cell malignancies, follicular dendritic cells, basal epithelial cells, and carcinomas. CD40 binds CD40 ligand (“CD40L”). CD40L is expressed on activated T cells during inflammation and cancer (Younes et al., 1998, Br. J. Haematol. 100:135-141; for a review see Grewal and Flavell, 1998, Annu. Rev. Immunol. 16:111-135). The interaction of CD40 with CD40L results in B cell activation and proliferation of normal B cells; however CD40-mediated signaling in B cell-derived tumor lines can result in activation-induced cell death. The strength of the activation signal is key to activation-induced tumor cell death (Grafton et al., 1997, Cell. Immunol. 182:45-56). Therefore, compositions and methods for increasing receptor-ligand interaction and strength of activation signal between CD40 and CD40L would be of great value in treating disease.